15 Chapte r: LTE Radio Interface Architecture Department of - - PowerPoint PPT Presentation

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15 Chapte r: LTE Radio Interface Architecture Department of - - PowerPoint PPT Presentation

Sep 12, 2023 377 likes •559 views

3G Evolution 15 Chapte r: LTE Radio Interface Architecture Department of Electrical and Information Technology Johan Lfgren 2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 1 Outline Architecture Basics Protocol

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Department of Electrical and Information Technology Johan Löfgren

3G Evolution

Chapte r:

2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 1

15

LTE Radio Interface Architecture

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2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 2

Outline

  • Architecture Basics
  • Protocol Architecture Overview
  • Short Description of Layers
  • Longer Descriptions

– Radio Link Control (RLC) – Medium Access Control (MAC) – Physical Layer (PHY)

  • Channels and Channel Mapping

– Logical Channels – Transport Channels – Physical Channels – Channel Mapping

  • Data Flow Example
  • Chapter Summary
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2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 3

Architecture Basics

  • LTE is strucutred into different protocol layers

– Lower protocol layers provide services for upper layers

  • The data from/to higher layers is known as a Service Data Unit (SDU)
  • The data from/to lower layers is known as a Protocol Data Unit (PDU)

– Each layer is responsible for different tasks

  • The upper layers should not have to care about the details
  • This structure is common to most modern systems

– Some layers are almost universal – Others are LTE specific

  • In LTE, IP packets enters through on of the SAE bearers

– SAE = System Architecture Evolution – The IP packets are then processed by the protocols

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2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 4

Protocol Architecture Overview

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2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 5

Short Description of Layers (1/2)

  • Packet Data Convergence Protocol (PDCP)

– Performs IP header compression

  • Reduces the number of bits to transmit over the radio

interfaced

  • Based on Robust Header Compression (ROHC)
  • Radio Link Control (RLC)

– Responsible for

  • Segmentation/concatenation
  • Retransmission handling
  • In-sequence delivery to higher layers

– Located in the eNodeB since no higher layers exists in LTE

  • In WCDMA this was handled higher in hierarchy
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Short Description of Layers (2/2)

  • Medium Access Control (MAC)

– Responsible for

  • Uplink/downlink scheduling
  • Hybrid-ARQ retransmissions
  • Choice of modulation
  • Resoucre assignment
  • Physical Layer (PHY)

– Responsible for

  • Coding/decoding
  • Modulation/demodulation
  • Resource mapping
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2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 7

Radio Link Control (RLC)

  • The RLC splits and concatenate the incoming data to fit the system

– The RLC PDU sizes are dynamically varied to fit the amount of data

  • Much data = long RLC PDUs to reduce RLC header overhead
  • Little data = short RLC PDUs to avoid too much padding
  • Responsible for error-free delivery to higher layers

– Accomplished with retransmission protocol – Re-sequencing of data may be requiered – Complementary to Hybrid-ARQ in lower layers

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2009-03-19 3G Evolution - HSPA and LTE for Mobile Broadband 8

Medium Access Control (MAC) (1/2)

  • Scheduling

– The basic operation is so-called dynamic scheduling

  • Downlink/Uplink are independently schedueled
  • Time-frequency resources dynamically shared between users
  • Each 1 ms TTI a new decision is taken
  • Each mobile unit scheduled by the eNodeB

– However each mobile still decides what radio bearer(s) to transmit

– Scheduling strategy is not specified by 3GPP

  • Implementation specific
  • Normally aiming at taking advantage of channel variations
  • Channel status report from mobile unit to eNodeB
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Medium Access Control (MAC) (2/2)

  • Hybrid ARQ with soft combining controlled by MAC

– Different simultaneous processes running – When error in one part, only that process needs to retransmit – Soft combining with adaptive coding leads to better chance of reception

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Physical Layer (PHY)

  • Responsible for

– Coding – PHY Hybrid ARQ processing – Modulation

  • Controlled by MAC

– Transport Format (TF)

  • Tells PHY modulation et c.

Simplified PHY processing

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Logical Channels

  • The MAC offers services to the RLC as logical

channels

– Broadcast Control Channel (BCCH)

  • System information to all mobile terminals

– Paging Control Channel (PCCH)

  • Paging information when searching a unit

– Common Control Channel (CCCH)

  • Random access information (setting up a connection)

– Dedicated Control Channel (DCCH)

  • User-specific control information (power/handover et c)

– Multicast Control Channel (MCCH)

  • Information needed for multicast reception

– Dedicated Traffic Channel (DTCH)

  • Transmission of user data

– Multicast Traffic Channel (MTCH)

  • Transmission of multicast data
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Transport Channels

  • The PHY offers services to the MAC as transport

channels

– Broadcast Channel (BCH)

  • Maps to BCCH

– Paging Channel (PCH)

  • To convey the PCCH

– Downlink Shared Channel (DL-SCH)

  • Main channel for downlink data transfer, used by many logical

channels

– Multicast Channel (MCH)

  • Used to transmit MCCh information to set up multicast

transmission

– Upink Shared Channel (UL-SCH)

  • Main channel for uplink data transfer, used by many logical

channels

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Physical Channels

  • The PHY transmit the data over the physical channels

– Physical Downlink Shared Channel (PDSCH)

  • Used for unicast transmission and paging

– Physical Broadcast Channel (PBCH)

  • Carries system information for accessing the network

– Physical Multicast Channel (PMCH)

  • Carries system information for multicast

– Physical Downlink Control Channel (PDCCH)

  • Carries mainly scheduling information

– Physical Hybrid ARQ Indicator Channel (PHICH)

  • Reports Hybrid ARQ status

– Physical Control Format Indicator Channel (PCFICH)

  • Information to enable the terminalse to decode the PDSCH

– Physical Uplink Shared Channel (PUSCH)

  • Uplink counterpart of PDSCH

– Physical Uplink Control Channel (PUCCH)

  • Sends Hybrid ARQ acknowledgement

– Physical Random Access Channel (PRACH)

  • Used for random access
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Channel Mapping

Downlink Channel Mapping Uplink Channel Mapping

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Data Flow Example

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Chapter Summary

  • LTE is structured into different protocol layers

– RLC is responsible for splitting and concatenation of data – MAC controls data and Hybrid ARQ – PHY is responsible for actual transmission

  • Different Channels are interfaces to higher layers

– Logical Channels – Transport Channels – Physical Channels